Cryoprotected surimi product

ABSTRACT

A surimi product comprising a surimi, and a hydroxypropyl starch hydrolyzate product, a spherical dextrose product, or a mixture thereof as a cryoprotectant, is disclosed. The cryoprotectant is present in a sufficient amount to prevent significant freeze-induced denaturation of proteins during storage of the surimi product, and thereby maintain protein functionality to allow use of the surimi product in the manufacture of foodstuffs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/009,646,filed on Jan. 27, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a method of preventing significantfreeze-induced denaturation of proteins in a surimi product duringstorage. More particularly, the present invention relates to a surimiproduct comprising a surimi and a sufficient amount of a hydroxypropylstarch hydrolyzate product, a spherical dextrose product, or a mixturethereof, as a cryoprotectant to prevent significant denaturation ofproteins during storage at freezing temperatures and thereby maintainprotein functionality. After thawing, a cryoprotected surimi productdemonstrates sufficient functionality for use in the manufacture offoodstuffs.

BACKGROUND OF THE INVENTION

Surimi is a generic term for minced fish that has been processed toremove bones, fish oil and fish flavor. Typically, surimi is prepared bythe fresh water leaching of mechanically deboned fish muscle. Theleached muscle, after dewatering, yields a light-colored, blandproteinaceous material comprising essentially myofibrillar (contractile)protein, or surimi.

Conventionally, surimi is produced from fish, such as Alaskan pollack,however surimi derived from poultry, pork and beef also are known. Withrespect to fish, surimi can be prepared at sea or on shore. Afterproduction, surimi usually is frozen into blocks, typically about 20kilograms in weight, and is stored for periods of weeks to months atfreezing temperatures before use.

Frozen surimi is an intermediate protein source used to produce variousfoodstuffs, such as, for example, imitation crab legs, imitationscallops, kamaboko (fish jelly) and imitation lobster. To produce asurimi-based foodstuff, the bland-tasting surimi first is thawed, thensalt is added to the thawed surimi during comminution of the surimi to apaste. The salt solubilizes the myofibrillar protein. Next, starch,non-muscle proteins (e.g., egg white, soy, whey), flavorings andcolorants are added to the surimi paste. The resulting paste is formedinto a desired shape (e.g., a crab leg), then heated to produce any of arange of foodstuff shapes and textures. The amount of surimi in suchfoodstuffs can range from 20% to 80% by weight of the foodstuff.

Fish species harvested to produce surimi often are available only farfrom shore and only during a short harvesting period. By necessitytherefore, some surimi is prepared at sea, and is frozen on shipboard topreclude spoilage before use. A majority of the surimi that is processedon shore is also frozen because most fish species are harvested during ashort harvesting period, but the demand for surimi is constantthroughout the year. Therefore, a sufficient amount of surimi producedon shore or at sea must be frozen to accommodate this year long demand.

As previously stated, surimi comprises essentially myofibrillarproteins. Fish myofibrillar proteins are very susceptible tofreeze-induced denaturation. Similar myofibrillar proteins derived frombeef, pork and poultry also are subject to freeze-induced denaturation,but to a lesser extent than fish myofibrillar proteins. To overcome thissusceptibility to protein denaturation, the refined myofibrillarcomponent of fish muscle, i.e., surimi, is admixed with a cryoprotectantprior to freezing the surimi. A cryoprotectant is a chemical compound,or combination of compounds, that prevents significant proteindenaturation and therefore imparts long-term storage stability to thefrozen surimi. This long-term storage stability in turn ensures goodprotein functionality to allow use of the surimi in the manufacture offoodstuffs.

The term "functionality" refers to the specific attributes a foodprocessor considers in adopting a protein source, like surimi, for usein a foodstuff. Functionality often is measured in terms of: (1) waterbinding ability to control water loss during storage, increased cookyield and increased juiciness; (2) fat binding ability to prevent fatseparation during cooking; (3) texture; (4) gelation temperature andstrength; (5) impact on appearance; and (6) impact on flavor and odor.As will be demonstrated in more detail hereinafter, functionality can beexpressed quantitatively as gel-forming potential, which is manifestedphysically as texture formation and water-binding ability.

In the absence of a cryoprotectant, a surimi stored at freezingtemperatures for extended periods has a decreased functionality. Thefreezing process causes ice crystal formation which results indehydration of the myofibrillar protein, a pH decrease, and a change insalt concentration. These three effects, in addition to varioushydrophobic interactions, denature and/or aggregate the frozenmyofibrillar protein of surimi. In addition, the longer the surimi isfrozen, the greater is the degree of protein denaturation.

Therefore, a cryoprotectant is added to the surimi to protect frozensurimi from a loss in functionality due to protein denaturing. Acryoprotectant must be intimately associated with the protein moleculesto prevent denaturing. Therefore, cryoprotectants are useful in a mincedproduct, like surimi, and are incorporated into the minced productbefore the product is frozen.

A cryoprotectant used to prevent significant denaturation of proteins infrozen surimi preferably meets several criteria. It is especiallyimportant for a cryoprotectant to maintain protein functionality duringextended frozen storage of surimi, and thereby allow use of the surimiin the manufacture of foodstuffs. It is also desired that acryoprotectant be relatively inexpensive, readily available, nontoxic,low in taste, water soluble, have good functional effects, and notappreciably brown the surimi during a cooking or heating process.Various proposed cryoprotectants have not met with commercial successbecause of their failure to meet one or more of these criteria. Suchmaterials include: carbohydrate compounds, like mono- anddi-saccharides; sugar alcohols; low molecular weight polyols; aminoacids; carboxylic acids; triglycerides; hydrogenated glucose syrups;surfactants, such as polyoxyethylene sorbitan esters and sucrose esters;and quaternary amines. Other cryoprotectants and mechanisms ofcryoprotection are discussed in G. A. McDonald et al., "Carbohydrates asCryoprotectants for Meats and Surimi", Food Technology, March, 1991, pp.150, 152-154, 156, and 158-159.

Presently, the standard, most widely used cryoprotectants for surimi aresucrose and sorbitol, either alone or in combination. In addition, arelatively small amount of a polyphosphate, such as sodiumtripolyphosphate, is conventionally added to the surimi as a synergistto increase the cryoprotective effect of sucrose and/or sorbitol.Sucrose and sorbitol are the cryoprotectants of choice for surimi, andespecially for Alaskan pollack surimi, because these cryoprotectants arereadily available, relatively economical, and importantly, have a lowtendency to cause Maillard browning when a surimi-based foodstuff iscooked or otherwise heated. Maillard browning is the well-known resultof a reaction between a reducing sugar and a protein to produce brownpigments. A cryoprotectant that effectively resists browning the surimiis very important with respect to the bright white kamaboko productscommonly served by the Japanese, the largest consumers of surimi.

Sucrose and sorbitol, however, add a definite sweet taste to surimi.Sucrose alone is a useful cryoprotectant but imparts too sweet of ataste to surimi. Therefore, sucrose usually is combined with sorbitol,in about a 1:1 weight ratio, and the mixture is used as a cryoprotectantfor surimi. The sucrose-sorbitol mixture still imparts a perceptiblesweet taste to surimi which is objectionable in many surimi-basedfoodstuffs. Therefore, it would be useful to provide a cryoprotectant:(1) that maintains the functionality of proteins in frozen surimi atleast as well as sucrose and sorbitol, (2) that has a low tendency tocause Maillard browning during storage of surimi at freezingtemperatures and during heating of a surimi-based foodstuff, and (3)that also possesses a low degree of taste.

In addition to sucrose and sorbitol, other specific cryoprotectantsadded to surimi include lactitol, maltose, fructose, lactose, mannitol,xylitol, lactilose, isomalt, maltitol, maltodextrin and various ediblegums. Another cryoprotectant for surimi is polydextrose, a polymerizedglucose which is a nonsweet, low calorie hydrolyzed starch bulking agentdisclosed in Lanier et al. U.S. Pat. No. 4,572,838, and usually is usedin combination with sorbitol. Yamamoto et al. U.S. Pat. No. 5,028,444also discloses a composition consisting essentially of sodiumbicarbonate, calcium citrate and calcium lactate that can be added tosurimi, prior to freezing and in addition to a cryoprotectant, toimprove the functionality of the frozen surimi.

Dextrose, in its conventional form of flat platelets, has also been usedas a cryoprotectant for surimi in an attempt to reduce the sweetnessimparted to surimi by sucrose. Dextrose, however, is also a reducingsugar and contributes to Maillard browning during cooking or heating ofa surimi-based foodstuff. Therefore, reducing sugars are consideredunsuitable cryoprotectants for a surimi that is processed into a lightor white-colored foodstuff.

Because cryoprotectants currently added to a surimi either impart anobjectionable sweet taste and/or significantly contribute to Maillardbrowning of the surimi-based foodstuff, there exists a need for animproved cryoprotectant that maintains the functionality of proteins ina frozen surimi, does not contribute significantly to Maillard browningduring storage at freezing temperatures and during heating, and is blandin taste. The present invention is directed to cryoprotectants thatprovide a surimi having good functionality, that resist Maillardbrowning and that have a bland taste.

SUMMARY OF THE INVENTION

The present invention is directed to surimi products comprising a surimiand a cryoprotectant. The cryoprotectant is present in an amountsufficient to prevent significant denaturation of the myofibrillarproteins in a surimi. In accordance with an important aspect of thepresent invention, the cryoprotectants of the invention do not impart anobjectionable sweet taste to a surimi, and do not significantlycontribute to Maillard browning of a surimi or a surimi-based foodstuffduring storage at freezing temperatures. Moreover, one of thecryoprotectant materials of the invention significantly resists Maillardbrowning of surimi and surimi-based foodstuffs even during cooking.

In particular, the surimi product comprises: (a) a surimi, and (b) asufficient amount of a hydroxypropyl starch hydrolyzate product, aspherical dextrose product, or a mixture thereof to cryoprotect thesurimi, and thereby maintain the functionality of the proteins in thesurimi after extended storage at freezing temperatures. A hydroxypropylstarch hydrolyzate product does not impart an objectionable sweet tasteto the surimi and does not contribute significantly to Maillard browningof the surimi, or a surimi-based foodstuff, during a heating or cookingprocess.

More particularly, the present invention is directed to a surimi productcomprising a surimi and from about 4% to about 12%, based on the weightof the surimi, of a hydroxypropyl starch hydrolyzate product. Apreferred hydroxypropyl starch hydrolyzate product has a dextroseequivalent (DE) of from about 1 to about 45, and is prepared by thecontrolled hydrolysis of hydroxypropylated starch. Even more preferably,the hydroxypropyl starch hydrolyzate product has a DE of from about 5 toabout 35.

Another important aspect of the present invention is to provide a surimiproduct comprising a surimi and from about 4% to about 12%, based on theweight of the surimi, of a spherical dextrose product. Dextrosepreviously was incorporated into a surimi as a cryoprotectant in theform of flat platelets. The spherical form of dextrose utilized in thepresent invention imparts excellent cryoprotection to surimi, andsurprisingly, does not significantly contribute to Maillard browningduring storage of surimi at freezing temperatures. A preferred dextroseproduct is a spherical form of dextrose having an average particle sizediameter of about 100 to about 1000 microns (μm), and a range ofparticle size diameters of about 50 to about 3000 μm.

In accordance with another important aspect of the present invention, ahydroxypropyl starch hydrolyzate product or a spherical dextrose productcan be used alone, or in combination, to cryoprotect a surimi. Thehydroxypropyl starch hydrolyzate product and/or spherical dextroseproduct also can be incorporated into the surimi with traditionalcryoprotectants, like sucrose or sorbitol, and synergists, likepolyphosphates.

Surimi products produced according to the invention are characterized bysufficient protein functionality such that, after extended storage atfreezing temperatures, the surimi product can be used in the manufactureof foodstuffs, like fabricated seafood products. Such productsdemonstrate an excellent functionality, e.g., an excellent ability toform gels after extended storage at freezing temperatures and subsequentthawing and processing. Protein gelation is the primary indicator ofprotein muscle functionality. The denaturation and degradation of fishproteins reduces gelation ability, and thereby reduces proteinfunctionality. Accordingly, surimi products of the present invention caneffectively bind water, fat and other foodstuff ingredients, and therebyprovide a foodstuff having a palatable texture. Surimi products of thepresent invention therefore can be processed into palatable foodstuffs.

BRIEF DESCRIPTION OF THE FIGURES

The above and other aspects and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments of present invention taken in conjunction with the drawings,wherein:

FIGS. 1-3 are plots of % Ca⁺² -ATPase activity vs. weight percent ofcryoprotectant, based on the weight of surimi, for unfrozen surimi andfor surimi subjected to freeze-thaw (F-T) cycles;

FIG. 4 is a plot of shear stress v. shear strain for unfrozen and fortwice frozen and thawed surimi samples either absent a cryoprotectant orincorporating a hydroxypropyl starch hydrolyzate product; and

FIGS. 5 and 6 are bar graphs illustrating the gel stress and gel strain,respectively, of surimi samples either including or absent acryoprotectant, and processed either at 25° C. and at 90° C. or only at90° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Surimi is the frozen concentrate of animal muscle tissue. Surimitypically is prepared from fish (fish surimi), and is used in themanufacture of foodstuffs like imitation crab, imitation scallops,imitation lobster and kamaboko. Surimi is also prepared from poultry(poultry surimi), pork (pork surimi) and beef (beef surimi).

Presently, the volume of surimi prepared from poultry, beef and pork issmall compared to the volume of surimi prepared from fish. Accordingly,the tests described hereinafter were performed on fish surimi, andparticularly, surimi prepared from Alaskan pollack. In addition, themyofibrillar proteins comprising fish surimi are less stable thansimilar proteins comprising mammalian and arian surimi, and accordinglyfish surimi is more susceptible to freeze-induced protein denaturation.Therefore, it is envisioned that the cryoprotectants useful in thepresent invention can be used in a surimi product derived from fish, aswell as a surimi derived from mammalian and avian sources such aspoultry, pork and beef. In particular, the cryoprotectants of thepresent invention can be used to prevent significant protein degradationin processed meat products. Such products include but are not limited tosausage, bologna, and hamburger wherein the processed meat is comminutedand mixed with cereals and other fillers.

In addition, although the tests described hereinafter are directed to afish surimi derived from Alaskan pollack, a hydroxypropyl starchhydrolyzate product or a spherical dextrose product, alone or incombination with each other or another cryoprotectant, also can be usedto cryoprotect a surimi derived from other fish species. Surimi derivedfrom Alaskan pollack presently is the largest volume fish surimi productand the economically most important. However, as supplies of Alaskanpollack become depleted and as other suitable fish species for surimiare accepted by consumers, the volume of surimi derived from fish otherthan Alaskan pollack is expected to increase. Nonlimiting examples offish surimi that can be cryoprotected by a hydroxypropyl starchhydrolyzate product or a spherical dextrose product include surimiderived from Alaskan pollack, Pacific whiting, Atlantic menhaden, atka,flat fish, cod, Soviet pollack, jack mackerel, Argentine hake,arrowtooth flounder, pink salmon, and sand trout.

Therefore, in accordance with the present invention, a surimi, andespecially a surimi derived from fish, is cryoprotected by incorporatinga sufficient amount of (1) a hydroxypropyl starch hydrolyzate product or(2) a spherical dextrose product into the surimi, prior to freezing, toprotect the surimi from freeze-induced protein denaturation. Acryoprotectant utilized in the present invention, i.e., a hydroxypropylstarch hydrolyzate product or a spherical dextrose product, is admixedwith the surimi in an amount of from about 4% to about 12% by weight ofthe surimi. Preferably, a cryoprotectant is admixed with the surimi inan amount of from about 6% to about 10% by weight of the surimi.

A hydroxypropyl starch hydrolyzate product useful as a cryoprotectant isprepared by hydrolyzing the reaction product of propylene oxide andstarch. The preparation of a hydroxypropyl starch hydrolyzate productuseful as a cryoprotectant for surimi is disclosed in Kesler et al.,U.S. Pat. No. 3,505,110, Quarles et al., U.S. Pat. No. 5,110,612, andQuarles et al., U.S. Pat. No. 5,294,453, each incorporated herein byreference.

Kesler et al. U.S. Pat. No. 3,505,110 discloses low calorie sugarproducts prepared by hydrolyzing hydroxypropylated starch. Thehydrolysis products principally comprise glucose and hydroxypropylatedpolysaccharides and include little or no (preferably less than 0.5%)maltose.

Quarles et al. U.S. Pat. No. 5,110,612 discloses preferred hydrolyzateproducts of hydroxypropylated starch that comprise greater than about15% by weight DP 2-6 hydrolyzate polymers and have a DE value of about20 to about 45. These hydrolyzate products have bulking agent propertiessimilar to those of sucrose in baked goods and other types of foodproducts.

The hydroxypropyl starch hydrolyzate products disclosed by Quarles etal. have a bitter off-flavor which can render these hydrolysis productsundesirable for particular food applications. The bitter off-flavor isattributed to hydrolysis products of hydroxypropyl starch hydrolysisproducts having molecular weights of about 200 to about 350 daltons(i.e., roughly between the molecular weights of glucose (180) andmaltose (342)) and are theorized to be one or more isomers of mono-, di-or tri-hydroxypropyl glucose. However, as will be demonstratedhereinafter, the bitter off-flavor of these hydrolysis products does notadversely affect a fish surimi because the bland, slightly fishy tasteof the surimi masks the bitter flavor of the hydroxypropyl starchhydrolyzate product. Quarles et al., U.S. Pat. No. 5,294,453, disclosesa hydroxypropyl starch hydrolyzate product having a reduced bitteroff-flavor.

Preferred hydroxypropyl starch hydrolyzate products for use in theinvention include those disclosed by Kesler et al., which have a DE ofabout 1 or greater, and are not too sweet tasting. Such products do notimpart an objectionable sweet taste to a surimi product, and thereforeovercome a disadvantage associated with traditional cryoprotectants,like sucrose.

Most preferred are hydroxypropyl starch hydrolyzate products preparedaccording to the method disclosed in Quarles et al. U.S. Pat. No.5,110,162. Such hydroxypropyl starch hydrolyzate products arecharacterized by DE values of from about 10 to about 45, and asufficient amount of DP 1 monomers and DP 2-6 hydroxypropyl starchhydrolyzate products to provide a hydroxypropyl starch hydrolyzateproduct that sufficiently cryoprotects frozen myofibrillar protein anddoes not impart an objectionable taste to the surimi, either too sweetor too bitter. Most preferred is a hydroxypropyl starch hydrolyzateproduct characterized by a DE of about 15 to about 30 and which also hasa DP 2-6 of about 15% to about 25% by weight, and a DP 1 of up to about10% by weight.

In accordance with another embodiment of the present invention, aspherical dextrose product also can be used to effectively cryoprotect asurimi. Dextrose, in its conventional form as flat platelets, has beenused previously to cryoprotect surimi, but significantly contributes toMaillard browning during storage of a surimi at freezing temperatures.For many foodstuffs, Maillard browning is undesirable, or unacceptable,because the consumer prefers, or demands, a white food product.

A spherical dextrose product not only cryoprotects a surimi, but incontrast to conventional dextrose products the surimi product alsoresists Maillard browning during storage at freezing temperatures. It istheorized, but not relied upon herein, that a spherical form of dextrosehas a better solubility and a greater ability to penetrate the surimiand intimately contact the myofibrillar proteins than does dextrose inits conventional form. In contrast, conventional dextrose productspreviously used as surimi cryoprotectants are flat, or planar, forms ofdextrose that had a tendency to remain on the surface of the surimi. Theconventional planar forms of dextrose impart an unacceptable brown colorto a surimi during storage at freezing temperatures. Unexpectedly, aspherical dextrose product does not significantly contribute to theMaillard browning of a surimi during storage at freezing temperatures.

In particular, a preferred spherical dextrose product useful as acryoprotectant for surimi has an average particle size diameter of about100 to about 1000 μm, and most advantageously about 150 to about 750 μm;and a range of particle size diameters of about 50 to about 3000 μm, andmost advantageously about 100 to about 1000 μm. A spherical dextroseproduct having an average particle size diameter of about 200 to about400 μm, and a range of particle size diameters of about 150 to about 500μm is sold under the tradename CRYO-DEX™, available from Penwest Foods,Englewood, Colo. CRYO-DEX™ is a spray dried spherical dextrose productincluding at least 99.5% by weight dextrose.

Conventional forms of dextrose comprise granules of which at least 80%by weight pass through a 60 mesh sieve. In contrast, CRYO-DEX™ sphericaldextrose comprises cocrystallized spherical dextrose granules whereinessentially no granules are retained on a 12 mesh sieve, and greaterthan 50% by weight of the granules are retained on a 60 mesh sieve, oralternatively stated, are greater than 250 microns (μm) in diameter.TABLE I compares the sieve analysis for CRYO-DEX™ spherical dextrose toa conventional dextrose product. In addition, a 20% by weight aqueoussolution of CRYO-DEX™ has a transmittance at 350 μm wavelength of atleast 80%, and has a pH of about 3.5 to about 5.5.

                  TABLE I                                                         ______________________________________                                        Sieve Analysis                                                                Product    on 20   on 40   on 60 on 100                                                                              through 100                            ______________________________________                                        CRYO-DEX ™                                                                            0.2     12.0    47.6  31.2  9.0                                    Commercial 0.5     2.6     11.7  46.5  38.7                                   Dextrose                                                                      ______________________________________                                    

A hydroxypropyl starch hydrolyzate product, a spherical dextroseproduct, or a mixture thereof, can be admixed with a surimi, prior tofreezing, to protect the surimi from freeze-induced protein degradation.A hydroxypropyl starch hydrolyzate product or a spherical dextroseproduct also can be used in conjunction with conventionalcryoprotectants, such a sucrose or sorbitol, to cryoprotect a surimi.The inclusion of a polyphosphate, like sodium tripolyphosphate,tetrasodium pyrophosphate or tetrapotassium pyrophosphate, as asynergist for the cryoprotectants, does not adversely affect thehydroxypropyl starch hydrolyzate product or the spherical dextroseproduct.

The total amount of cryoprotectant added to a surimi is generally fromabout 4% to about 12% by weight of the surimi. Preferably, the totalamount of cryoprotectant added to the surimi is from about 6% to about10% by weight of the surimi. A polyphosphate synergist is included in anamount of up to about 1% by weight of the surimi.

To demonstrate the usefulness of the present invention, a hydroxypropylstarch hydrolyzate product or a spherical dextrose product wasincorporated into a fish surimi and tested for: (1) an ability tocryoprotect frozen surimi, (2) an ability to maintain the functionalityof proteins in surimi that has been stored below freezing temperatures,(3) an ability to resist Maillard browning during storage at freezingtemperatures or during a heating process, and (4) an ability to avoidimparting a sweet or an off-taste to the surimi or a surimi-basedfoodstuff.

In the tests described hereinafter the hydrolyzed hydroxypropyl starchhydrolyzate product utilized as a cryoprotectant was prepared inaccordance with the methods disclosed in Quarles et al. U.S. Pat. No.5,110,612 and had a DE of about 24.4, a DP 2-6 of about 17.8% by weightand a DP 1 of about 9.6% by weight. The spherical dextrose productutilized as a cryoprotectant was CRYO-DEX™, a spherical dextrose havingan average particle size diameter of about 200 to about 400 μm, andavailable from Penwest Foods Co., Englewood, Colo.

EXAMPLE 1

In this example, the ability of a hydroxypropyl starch hydrolyzateproduct or a spherical dextrose product to cryoprotect a surimi wascompared to the ability of sucrose, an industry standard, to cryoprotecta surimi. In the first of these comparative tests, a model fish protein(actomyosin) was frozen and thawed under controlled conditions todetermine the effectiveness of a hydroxypropyl starch hydrolyzateproduct or a spherical dextrose product as a cryoprotectant. In thiscomparative test, Ca⁺² -ATPase activity was determined after freezingand thawing a test sample. It is known to those skilled in the art thatCa⁺² -ATPase activity correlates well with protein functionality in asurimi, i.e., that a high Ca⁺² -ATPase activity indicates good proteinfunctionality.

The results of these comparative tests are illustrated in the plots ofFIGS. 1 through 3. In each of FIGS. 1 through 3, the ordinate (Y-axis)plots the % Ca⁺² -ATPase activity of the fish protein and the abscissa(x-axis) plots the percentage by weight of cryoprotectant incorporatedinto the surimi. In each of FIGS. 1 through 3, the % Ca⁺² -ATPasedecreases with an increasing concentration of cryoprotectant forunfrozen (unF-T) surimi samples. This decrease is an artifact thatindicates a decreased Ca⁺² -ATPase activity, but is not related toactual protein denaturation.

With respect to FIG. 1, sucrose, the industry standard, exhibits goodcryoprotectancy as demonstrated by the increasing % Ca⁺² -ATPaseactivity for surimi samples that include an increasing amount of sucroseand that have been subjected to a freeze-thaw cycle (F-T). FIGS. 2 and 3similarly demonstrate an increase in % Ca⁺ -ATPase activity for a surimisample cryoprotected with either a spherical dextrose product or ahydroxypropyl starch hydrolyzate product, respectively. Both FIGS. 2 and3 illustrate a direct relationship between % Ca⁺² -ATPase and weightpercent of cryoprotectant, thereby showing that, like sucrose, aspherical dextrose product or a hydroxypropyl starch hydrolyzate producteffectively cryoprotect fish protein against freeze-induceddenaturation.

The slope of the F-T (freeze-thaw) plot of FIG. 1 (sucrose), a wellknown cryoprotectant, approximates the slope of the F-T plot in FIGS. 2and 3, thereby indicating to a person skilled in the art that sucrose, ahydroxypropyl starch hydrolyzate product, and a spherical dextroseproduct are effective cryoprotectants. However, it also is known tothose skilled in the art that sucrose imparts too sweet of a taste to asurimi and to foodstuffs derived therefrom, and therefore cannot be usedat high levels. Conventionally, sucrose is used at a level of about 4%by weight of the surimi, in conjunction with sorbitol, as acryoprotectant. The cryoprotectants utilized in the present invention donot possess the disadvantage of relatively unacceptable sweetness andtherefore can be used at high levels without the need to incorporatesorbitol to reduce sweetness. A spherical dextrose product is lower insweetness compared to sucrose and therefore helps overcome the sweetnessproblem associated with sucrose. A hydroxypropyl starch hydrolyzateproduct has essentially no sweetness, and its slight bitter off-taste ismasked by the bland taste of surimi.

EXAMPLE 2

In this example, a set of tests compared the gelling properties of ahydroxypropyl starch hydrolyzate product to sucrose. Protein gelation,as measured by gel-forming ability, is a primary indicator of muscleprotein functionality. The most informative method for both measuringand specifying the gel-forming properties of fish protein, and otherproteins as well, is through a torsional measurement of both: (1) thestrain to gel failure and (2) the rigidity (calculated from stress andstrain to failure measurements) of heat-induced gels prepared bystandardized procedures. The plotting of these torsional measurements(shear stress v. shear strain) reveals the general sensory properties ofthe gel. The stress and strain tests are fully explained in J. W. Parket al., J. Food Sci., 52(3), (1987), pp. 537-542.

FIG. 4 illustrates common sensory terms used to describe the texture ofgels falling in the regions of the four "corners" of a shear stress v.shear strain plot. The human mouth is able to perceive, in general, therelative ratio of rigidity, or stiffness, (i.e., shear stress) tocohesiveness of a product (i.e., shear strain). A higher value for thisstress to strain ratio translates into a "brittle", or friable,sensation, while a low value for the stress to strain ratio translatesto a "rubbery" texture. In gels wherein a relative balance existsbetween the gel stress and gel strain, the overall magnitude of the twotextural parameters (rigidity and cohesion) place the textural sensationon a continuum moving from a perception of "soft", or "mushy", upwardsto a perception of "toughness".

FIG. 4 also illustrates the results of incorporating a hydroxypropylstarch hydrolyzate product produced according to the methods of Quarleset al. U.S. Pat. No. 5,110,612 and having a DE of about 24.4 and a DP2-6 of about 17.8% by weight into a surimi that is used in thepreparation of an imitation crabstick.

    ______________________________________                                        Cryoprotected Surimi                                                          ______________________________________                                        Surimi derived from                                                                            96% (by weight)                                              Alaskan Pollack                                                               Hydroxypropyl Starch                                                                            4% (by weight)                                              Hydrolyzate Product                                                           (D.E. about 24.4, D.P.                                                        2-6 about 17.8%)                                                              ______________________________________                                    

The results of shear stress and shear strain tests on the surimicryoprotected with a hydroxypropyl starch hydrolyzate product werecompared to stress and strain tests on a surimi that did not include acryoprotectant (control sample). An unfrozen portion of the controlsurimi and of the cryoprotected surimi were each formed into animitation crabstick by admixing the surimi with standard foodstuffingredients. A second portion of the control surimi and thecryoprotected surimi were each twice frozen and thawed prior to admixingwith standard foodstuff ingredients and shaping into an imitationcrabstick. The ability of the various surimi samples to form gels wasdetermined by measuring shear stress (gel hardness) and shear strain(gel cohesiveness) by standard procedures known to those skilled in theart.

The results of the shear stress and shear strain tests for the unfrozenand freeze-thawed surimi samples are plotted in FIG. 4. From FIG. 4, thecontrol surimi sample (i.e., including no cryoprotectant) showed asignificant decrease in gelling properties (i.e., a softer product)after the control surimi sample was twice frozen and thawed. Incontrast, by adding 4% by weight of a hydroxypropyl starch hydrolyzateproduct to the surimi, the unfrozen cryoprotected surimi of was notadversely affected compared to the control sample (both are at theessentially identical position of the plot). In addition, thecryoprotectant utilized in the present invention prevented significantprotein degradation and therefore maintained the functional propertiesof the surimi. The twice frozen and thawed cryoprotected surimi, whichincluded a hydroxypropyl starch hydrolyzate product, provided a gelhaving significantly improved properties compared to the twice frozenand thawed control sample.

EXAMPLE 3

In this example, further tests were performed on surimi prepared fromAlaskan pollack. FIGS. 5 and 6 illustrate the stress (gel strength) andstrain (gel cohesiveness), respectively, of various surimi gels, whicheither include or are lacking a cryoprotectant. The strength andcohesiveness of the gels were measured by standard techniques on aTorsion Gelometer for torsional failure (twisting until breakage). Thegel stress and gel strain illustrated by the bar graphs in FIGS. 5 and6, respectively, were measured for each surimi sample after portions ofthe surimi sample were subjected to one of a different set ofconditions. For example, a portion of each surimi sample was testedprior to freezing and a second portion of each surimi sample was testedafter undergoing a freeze-thaw (FT) cycle. In this test, the frozensurimi samples were stored at -20° C. for two weeks. The gellingproperties for each surimi sample also were tested after processing aportion of a surimi sample at 90° C. (a pasteurization cook) for onehour, or after preprocessing a portion of a surimi sample at 25° C. for15 minutes followed by processing at 90° C. for one hour.

The bar graphs in FIGS. 5 and 6 therefore are derived from fivedifferent surimi samples:

Product 3A

The control sample did not include a cryoprotectant, but 4% sucrose (byweight), 4% sorbitol and 0.3% sodium triopolyphosphate was added to thecontrol sample prior to testing and after thawing (for freeze-thawedsamples) in order to use gel measurements as a measure of proteindenaturation during frozen storage.

Product 3B

An Alaskan pollack surimi including 8% sorbitol, by weight, as acryoprotectant and 0.3% sodium tripolyphosphate as a cryoprotectantsynergist.

Product 3C

An Alaskan pollack surimi including 8% hydroxypropyl starch hydrolyzateproduct (D.E. about 24.4, D.P. 2-6 about 17.8%), by weight, as acryoprotectant and 0.3% sodium tripolyphosphate as a cryoprotectantsynergist.

Product 3D

An Alaskan pollack surimi including 4% sorbitol and 4% sucrose, byweight, as a cryoprotectant and 0.3% sodium tripolyphosphate as acryoprotectant synergist.

Product 3E

An Alaskan pollack surimi including 8% spherical dextrose product(CRYO-DEX™), by weight, as a cryoprotectant and 0.3% sodiumtripolyphosphate as a cryoprotectant synergist.

The bar graphs of FIGS. 5 and 6 illustrate that the Product 3A controlexhibited significantly poorer gel performance than any of thecryoprotected samples even after a relatively short two week storageperiod at freezing temperatures. This result illustrates the overallneed to cryoprotect frozen surimi. For portions of the surimi samplesthat were not frozen, the gelling ability for the four cryoprotectedsamples was approximately the same. For pollack surimi, gels preset at25° C. typically exhibit higher stress values that gels than are notpreset, and exhibit strains that are very similar. These results areillustrated in FIGS. 5 and 6 as the unshaded or lightly-shaded bars.

Other portions of the surimi samples were subjected to a six cyclefreeze-thaw process of 24 hours storage in a 4° C. cooler followed by 24hours storage in a -20° C. freezer, repeated six times. This cyclicalfreeze-thaw process accelerates the protein denaturation process thatoccurs over long-term storage at freezing temperatures. FIGS. 5 and 6illustrate that the gel strain and gel stress became unmeasurable for asurimi (Product 3A) that does not include a cryoprotectant and that issubjected to a cyclical freeze-thaw cycle. In terms of texture, theprocessed surimi lacking a cryoprotectant (Product 3A) was too soft andmushy to grind and test on the torsion equipment. In general, this soft,mushy surimi has a strain of less than 0.5. A high quality surimitypically exhibits a strain of about 1.7 to about 2.6 after frozenstorage.

The four surimi samples including a cryoprotectant (Products 3B-3E) eachprovided gels having excellent gel stress and gel strain measurements.Both the hydroxypropyl starch hydrolyzate product (Product 3C) and thespherical dextrose product (Product 3E) demonstrated an ability tocryoprotect surimi at least as well as the standard cryoprotectants(e.g., sorbitol or sucrose/sorbitol, as in Products 3B and 3D,respectively, used in the industry. Both the hydroxypropyl starchhydrolyzate product and the spherical dextrose product providedcryoprotected surimi products (Products 3C and 3E, respectively) thatshowed essentially no change in gel stress or gel strain due tofreeze-thaw cycling. The bar graphs clearly show that the stress andstrain for cryoprotected surimi samples of Products 3C and 3E areessentially identical for unfrozen portions of the samples and forportions of the samples subjected to freeze-thaw cycles. In comparison,surimi samples cryoprotected with sorbitol (Product 3B), or acombination of sucrose and sorbitol (Product 3D), demonstrated adecrease in gel stress and gel strain after freeze-thaw cycling. Adecrease in gel strain is indicative of a decrease in the functionalqualities of the protein. Accordingly, a hydroxypropyl starchhydrolyzate product or a spherical dextrose product effectivelycryoprotects fish surimi and prevents significant protein denaturationduring long storage periods at freezing temperatures.

Visual and taste tests performed in conjunction with the above-describedtests also demonstrated that a surimi cryoprotected with a sphericaldextrose product has more clarity and sheen, and less sweetness, than asurimi cryoprotected with sucrose. A hydroxypropyl starch hydrolyzateproduct has essentially no sweet taste, and can have a slightly bitteroff-taste. A surimi cryoprotected with a hydroxypropyl starchhydrolyzate product, however, does not have a sweet taste or a slightlybitter off-taste. The taste of the hydroxypropyl starch hydrolyzateproduct is masked by the natural taste of the surimi. The lack ofsweetness and lack of a bitter off-taste is an advantage because noartificial taste is imparted to the surimi, and the natural flavor ofsurimi is preferred by a majority of consumers.

In addition to use as a cryoprotectant, a hydroxypropyl starchhydrolyzate product or a spherical dextrose product also can be used inshipboard mincing processes to preventing significant proteindecomposition of unfrozen minced fish, and thereby allow furtherprocessing of the unfrozen mince on shore. The cryoprotectants utilizedin the present invention also can be used to protect beef, pork orpoultry surimi, or processed meats, from significant proteindenaturation during long storage periods at freezing temperatures.

Obviously, many modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated by the appended claims.

What is claimed is:
 1. A surimi product comprising a surimi and asufficient amount of a hydroxypropyl starch hydrolyzate product tocryoprotect the surimi and maintain functionality of proteins in thesurimi, wherein the hydroxypropyl starch hydrolyzate product has a DE offrom about 5 to about
 35. 2. The surimi product of claim 1 wherein thesurimi is beef surimi, pork surimi, poultry surimi, fish surimi, or amixture thereof.
 3. The surimi product of claim 1 wherein the surimi isfish surimi.
 4. The surimi product of claim 1 wherein the hydroxypropylstarch hydrolyzate product is present in an amount of from about 4% toabout 12% by weight of the surimi.
 5. The surimi product of claim 1wherein the hydroxypropyl starch hydrolyzate product has a DP 2-6 offrom about 15% to about 25%.
 6. The surimi product of claim 1 furthercomprising a member selected from the group consisting of sucrose andsorbitol.
 7. The surimi product of claim 1 further comprisingpolyphosphate as a synergist for the hydroxypropyl starch hydrolyzateproduct.
 8. The surimi product of claim 1 wherein the hydroxypropylstarch hydrolyzate product has a DE of about 15 to about
 30. 9. Thesurimi product of claim 8 wherein the hydroxypropyl starch hydrolyzateproduct has a DP 2-6 of about 15% to about 25% by weight and a DP 1 ofup to about 10% by weight.
 10. A surimi product comprising a surimi anda sufficient amount of a hydroxypropyl starch hydrolyzate product tocryoprotect the surimi and maintain functionality of proteins in thesurimi, wherein the hydroxypropyl starch hydrolyzate product has a DE ofabout 24.4 and a DP 2-6 of about 17.8% by weight.
 11. The surimi productof claim 10 having a DP 1 of about 9.6% by weight.